1. Field of the Invention
The present invention relates to a brake-transmission shift interlock device for an automatic transmission system and more particularly, to a device that includes a solenoid having a two part plunger with an exterior second portion of the plunger positioned to prevent movement of a transmission member thereby preventing operation of the transmission shifter until the brake is depressed.
2. Background of the Prior Art
Automatic transmissions are commonly used for controlling the modes of operation of an automobile including park, drive, reverse and neutral. The modes of operation are selected by moving a shifter, integrally mounted to the automatic transmission, to a position corresponding to the indicated mode. These modes of operation have simplified a driver's task when operating an automobile. However, experience has shown that it is possible for an automatic transmission to "slip" from a park mode to a drive mode without the driver moving the shifter, thereby compromising safety and possibly developing into a collision involving the automobile and an adjacent structure.
A well-known method in the art of correcting aforementioned problem is to employ an interlock device that allows the automatic transmission shifter to move from the park mode only when the automobile engine is running and the brake pedal is depressed. The interlock also allows the shifter to be moved back to the park mode irrespective of the shifter positions.
A well-known interlock device that accomplishes the above objective utilizes a solenoid such that when in a de-energized state, prevents movement of the transmission shifter, and when energized (by depressing the brake pedal) allows the shifter to move from the park position. To minimize the required lineal force to operate the solenoid thereby reducing the size of the solenoid, the solenoid was designed such that the travel of an internal plunger component of the solenoid, occurred in a horizontal line to minimize the effects of gravity on the plunger.
Although effective in correcting the above-stated problem, prior art interlocking devices were required to use relatively large solenoids to provide sufficient lineal force to overcome the binding of internal solenoid components caused by an external "blocking" component joined to a plunger component of the solenoid. The blocking component being utilized to impede the travel of a preselected transmission member thereby preventing operation of the transmission. These relatively large solenoids generate undesirable noise when operated and use components that "wear down" relatively quick. Examples of prior art designs are illustrated in U.S. Pat. Nos. 5,379,872; 5,309,744; 5,293,763; 5,150,593; 5,036,962; 4,983,960; 4,638,279; and 1,768,518.
Therefore, a solenoid operated interlocking device is required that has less binding between internal solenoid components, requires less lineal force to operate, is relatively smaller in size and generates less noise than the prior art solenoids.